[PATCH v7 2/7] arm64: mm: Move fixmap region above vmemmap region

[Ard Biesheuvel]

From: Ard Biesheuvel <ardb at kernel.org>

Move the fixmap region above the vmemmap region, so that the start of
the vmemmap delineates the end of the region available for vmalloc and
vmap allocations and the randomized placement of the kernel and modules.

In a subsequent patch, we will take advantage of this to reclaim most of
the vmemmap area when running a 52-bit VA capable build with 52-bit
virtual addressing disabled at runtime.

Note that the existing guard region of 256 MiB covers the fixmap and PCI
I/O regions as well, so we can reduce it 8 MiB, which is what we use in
other places too.

Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
---
 arch/arm64/include/asm/memory.h  | 2 +-
 arch/arm64/include/asm/pgtable.h | 2 +-
 arch/arm64/mm/fixmap.c           | 3 +++
 arch/arm64/mm/ptdump.c           | 4 ++--
 4 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index 99caeff78e1a..2745bed8ae5b 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -51,7 +51,7 @@
 #define VMEMMAP_END		(VMEMMAP_START + VMEMMAP_SIZE)
 #define PCI_IO_START		(VMEMMAP_END + SZ_8M)
 #define PCI_IO_END		(PCI_IO_START + PCI_IO_SIZE)
-#define FIXADDR_TOP		(VMEMMAP_START - SZ_32M)
+#define FIXADDR_TOP		(-UL(SZ_8M))
 
 #if VA_BITS > 48
 #define VA_BITS_MIN		(48)
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index b19a8aee684c..8d30e2787b1f 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -22,7 +22,7 @@
  *	and fixed mappings
  */
 #define VMALLOC_START		(MODULES_END)
-#define VMALLOC_END		(VMEMMAP_START - SZ_256M)
+#define VMALLOC_END		(VMEMMAP_START - SZ_8M)
 
 #define vmemmap			((struct page *)VMEMMAP_START - (memstart_addr >> PAGE_SHIFT))
 
diff --git a/arch/arm64/mm/fixmap.c b/arch/arm64/mm/fixmap.c
index c0a3301203bd..6fc17b2e1714 100644
--- a/arch/arm64/mm/fixmap.c
+++ b/arch/arm64/mm/fixmap.c
@@ -16,6 +16,9 @@
 #include <asm/pgalloc.h>
 #include <asm/tlbflush.h>
 
+/* ensure that the fixmap region does not grow down into the PCI I/O region */
+static_assert(FIXADDR_TOT_START > PCI_IO_END);
+
 #define NR_BM_PTE_TABLES \
 	SPAN_NR_ENTRIES(FIXADDR_TOT_START, FIXADDR_TOP, PMD_SHIFT)
 #define NR_BM_PMD_TABLES \
diff --git a/arch/arm64/mm/ptdump.c b/arch/arm64/mm/ptdump.c
index 46acb2a24da0..a929b5a321db 100644
--- a/arch/arm64/mm/ptdump.c
+++ b/arch/arm64/mm/ptdump.c
@@ -45,12 +45,12 @@ static struct addr_marker address_markers[] = {
 	{ MODULES_END,			"Modules end" },
 	{ VMALLOC_START,		"vmalloc() area" },
 	{ VMALLOC_END,			"vmalloc() end" },
-	{ FIXADDR_TOT_START,		"Fixmap start" },
-	{ FIXADDR_TOP,			"Fixmap end" },
 	{ VMEMMAP_START,		"vmemmap start" },
 	{ VMEMMAP_END,			"vmemmap end" },
 	{ PCI_IO_START,			"PCI I/O start" },
 	{ PCI_IO_END,			"PCI I/O end" },
+	{ FIXADDR_TOT_START,		"Fixmap start" },
+	{ FIXADDR_TOP,			"Fixmap end" },
 	{ -1,				NULL },
 };
 
-- 
2.43.0.472.g3155946c3a-goog